The prior art provides various wheels for use in the various industries designed to satisfy the requirements presented by the environment within which such wheels are used and the vehicles to accomplish desired objectives. The variety of such wheels is illustrated by the following patents.
U.S. Pat. No. 2,497,224 discloses a roller wheel composed of a synthetic resin impregnated with resilient filler material and a dry lubricant for use with drawers in metal equipment.
U.S. Pat. No. 3,199,364 relates to composite gears, sprockets and pulleys formed by injection molding of different plastic materials without metal components therein.
U.S. Pat. No. 3,578,818 pertains to a rubber tire attached to a plastic molded wheel by various attaching, interlocking elements so that the two components cannot separate under operating conditions by skid, lateral or radial forces or flexing of the tire under load.
U.S. Pat. No. 4,019,789 relates to a plastic-metallic trolley wheel assembly used in the food processing industry where high heat and moisture conditions exist and the trolley wheel assembly must bear high loads. The assembly comprises: a plastic fire or trolley wheel having a central opening and an annular outer metallic bearing race positioned on the wheel adjacent to the opening. Means are provided to hold the wheel and the metallic bearing race to prevent separation thereof.
U.S. Pat. No. 4,071,279 describes a solid polyurethane tire suitable for use on vehicles adapted for transportation of goods within industrial manufacturing plant facilities. The polyurethane is prepared by reacting a complex of 4,4'-methylene dianiline and a salt with a prepolymer of selected diisocyanates and selected polyester polyols and polyethylene polyols.
U.S. Pat. No. 4,535,827 discloses a molded shock-absorbing wheel assembly used in the automotive industry in assembly line operations, the wheel assembly comprising: a cast iron annular core member disposed concentrically about a bearing seat; and a plastic material, such as polyurethane covering the core member. Means are included to prevent relative sliding movement between the core and the plastic material.
The present invention concerns the reduction or elimination of iron and other metals, the presence of which in the working environment where photographic film base is produced adversely affects the film base. In particular, the invention concerns the replacement of steel wheels with plastic clad steel wheels for monorail trolley systems which are used to convey rolls of polymeric webs such as acetate and polyester webs which require extreme cleanliness during the manufacture and moving from one place to another on production floors.
The problems associated with the production of photographic film base will be appreciated from a brief description of such production. Photographic emulsions are coated on polymeric webs such as acetate and polyester for support. The polymer supports are manufactured in wide webs which are coiled into a roll weighing more than 1000 lb. each. A multiple of these rolls is carried by a monorail trolley from the web manufacturing location to a succession of manufacturing stations. At the final stage, photographic emulsions are applied onto the supports. Extreme care must be taken during all the steps of manufacturing process and the web handling so that the final product is clean and defect-free. Furthermore, extreme caution must be taken to insure that photo active particles do not contaminate the products. Iron and iron compounds, aluminum, and silicone are some examples of photo-active contaminants.
There are many moving and stationary components in a monorail system that are made of steel. Wear debris and corrosion products of those components are the source of detrimental iron and iron compounds. The largest amounts of iron debris are produced when the steel wheels of trolleys slide over the stationary monorail track at a speed greater than 30 feet per minute. Although extreme care is taken to clean the rail tracks, wheels and other components of monorail trolleys, it is difficult to completely eliminate contamination. In a typical manufacturing operation there are eight load bearing cast steel wheels in each trolley carrying more than 4000 lbs. of photographic support rolls. The loaded trolleys typically move at speeds greater than 30 feet per minute over the stationary rails and generate a great deal of wear debris. In addition, there are generally sixteen steel guide rollers in each trolley that ride against the edge of the rail generating additional iron debris.
Steel is a very common engineering material for constructing heavy equipment such as monorail trolleys. It is difficult to substitute steel with other engineering materials cost-effectively without sacrificing robustness. Since neither the rails nor the wheels can be lubricated to reduce or eliminate wear, the task of eliminating iron contamination is extremely difficult. Furthermore, as indicated, other engineering materials such as aluminum, copper or brass cannot be used since they are photo-active.
The prior art offered no satisfactory solution to these problems.